Aluminous sintered parts and techniques for fabricating same



Jan. 31, 1967 s. sToRcHHElM 3,301,671

ALUMINOUS SINTERED PARTS AND TECHNIQUES FOR FABRICATING SAME Filed March I5, 1964 /Jaoy //m A/vo lj/mou Mmes/UM 7725759195 0.090 /fycf/fs 7//CK 4% A Ursl loo Samana/yf D iowa-8% www1/Zen B 075-35800 H4 ome-6s 46m/G Cowes F0@ 4% @owe-Q5 Aww/yan Tl E Mera? 00E/VGH@ United States Patent C) 3,301,671 ALUMNOUS SHNTIERED PARTS AND TECH- NQUES FR FABRTCATING SAME Samuel-Storehheim, Forest Hills, NX., assigner to Alloys Research & Manufacturing Corporation, Woodside,

NX., a corporation of Delaware Filed Mar. 3, 1964, Ser. No. 349,123 11 Claims. (Cl. 75-200) This application is a continuation-in-part of my copending application, Serial No. 276,476, filed Apr. 29, 1963, and now abandoned,

This invention relates generally to powder-metallurgical techniques for fabricating aluminous products, including such high density parts as gears, cams, sprockets and the like. An important aspect of the invention vresides in techniques and materials for so manipulating the crystal lattice or atomic varray structure of aluminous products as to counterbalance shrinkage effects arising in sintering by reason of certain alloying constituents, with expansion effects introduced lby other alloying constituents, so as to produce distortion-free, aluminous products having exceptional mechanical properties and response to heat treatment.

The term aluminous as used herein is intended to cover elemental aluminum and alloys in which aluminum is the dominant element, as well as mixture of metallic particulates wherein the major component of the mixture is elemental aluminumvor an aluminum-based alloy. The term particulates as used herein is intended to encompass metal particles of powder size (i.e., up to 1000` microns) and particles of colarse size, as well as various particle shapes such as needles, fibers, shot, pellets and scrap turnings.

One major problem encountered in sintering powder- Vmetallurgical components which are either loose-packed or green-compressed, is due to dimensional changes occurring during the sintering operation. Such changes, which are sometimes erratic, may because of contraction effects result in excessive or nonuniform shrinkage of the part, or give rise to an irregular expansion. Consequently, during production runs many partshave to be scrapped, with resultant losses. Moreover, where the partisan assembly component, a production line using this component may have to be halted until satisfactory parts can be obtained.

In the'copending applications of Storchheim, Ser. No. 150,826, tiled Nov. 7, 1961, now Patent No. 3,232,754, and Ser. No. 210,072, led July 16, 1962, and now abandoned, there are disclosed novel methods for fabricating aluminum-based high and low density parts. In the processes disclosed in these applications, a blend is rst formed of aluminum `and copper powders, the copper content in the mixture lbeing in the range of 1% to 8% by weight. (Other alloy type alloy mixes can be made too; i.e., Al-Mg, Al-Si, etc.) This mixture is then compressed into a green compact and thereafter rapidly heated and sintered in a reducing or protective atmosphere.

I have 4found with aluminum powder rnetallurg such as when the starting mixture is aluminum and copper, or even pure Al, that dimensional control `becomes difcult to maintain. The reason for this is that in the former case, as the relative copper content is raised, the amount of liquid phase present in the alloy during Ahigh-temperature sintering also increases, and as a consequence the part tends to distort during this opera-tion. Nevertheless, a high copper content is desinable in that higher strengths are obtainable. But even pure Al shows shrinkage which can be objectionable,particularly if low density structural parts are Wanted. to counter shrinkage of the sintered part is desirable.

Accordingly it is the main object of this invention to provide a technique for alloying and fabricating aluminous In this instance a high expansion force v powder-metallurgical parts containing for example Mg, wherein expansion forces during sintering of loose particles or green compacts counterbalance shrinkage forces in the course of sintering to produce parts having desired uniform, reproducible and predictable dimensions and properties.

For a better understanding of the invention, reference is made to the following detailed description to be read in conjunction with the accompanying drawings, wherein:

FIGURES 1 to 3 are curves illustrating the effect of certain additives on the characteristics 4of an aluminous product made by powder metallurgical techniques in accordance with the invention.

At the outset, it is important to recognize that the formation of any liquid phase, as for example in certain powder metallurgy reactions, almost universally (there are a few minor exceptions) is accompanied by a volume expansion over land above that which exists for the materials in their previous solid state. Thus, even the addition of copper to aluminum will cause the formation of higher volumed liquid phases over the solid elementals entering the reaction and can cause the powder compacts to expand. However, the amount of liquid phase expansion is substantia-lly less than that of low density constituents added to aluminum las per magnesium, etc., reacting with aluminum and forming a liquid phase. Thus we have considerably greater expanding forces with regard to aluminum-magnesium vs. aluminum-copper as the solid constituents enter into the alloy fluid.

The benefits of the expansion with magnesium are realized two Ways: One is that during solidioation, the magnesium which has gone into solid solution with the taluminum expands the crystal lattice structure as shown in Table A below. This in turn can aid in counter-balancing shrinkage forces during sintering. This is not true of aluminum-copper, because in this instance the copper entering in solution with the aluminum contnacts the atomic lattice, .also as shown in Table A and aids the shrinkage forces of sintering. Note too, from Table A that such elements as zinc contract the atomic lattice. Thus, one can achieve an eiect similar to the one described in the case of copper through use of zinc addition, the zinc being added `in the foirn of an elemental powder or in combination with copper as brass ake or powder.

-` Expansion.

The second point is the fact that magnesium and its alloys appear to be most sensitive (as addition agents in aluminum) to the sintering conditions versus copper iadditions to aluminum. For the same dew-point, there apparent-ly is an accelerated oxidation (non-reducible) ofthe sintering compact which ri gidizes said compacts against the shrinkage forces of the sintering operation. This is not true as to the magnitude of rigidizing tior the Aaluminumcopper alloys, therefore there is less inhibition or resistance to the shrinkage forces.

It should be noted that this effect of magnesium additions can vary depending upon the characteristics of the aluminum powders used in the lend. Thus for the same sintering conditions where relatively coarse aluminum powders containing about 35 w/o -325 mesh material are used the net effect of magnesium additions Will,

as already discussed, be to expand the compact; where relatively fine aluminum powders containing about 90 w/o -325 mesh material are used the net effect will be to contract the compact. In those instances where coarse powders are used, the sintering and shrinkage rates are relatively low so that rigidization of the compact against shrinkage forces occurs before the compact can contract sufficiently to show a net shrinkage after sintering. Where finer powders are used, the sintering and shrinkage rates are relatively high and apparently a net shrinkage can result before rigidization due to oxidation sets in. Thus line powders can be used to advantage when the sintering atmosphere is poor, i.e., has a high dew point. The sintered product produced under such conditions will exhibit greater shrinkage, better alloying and ibetter properties than 'will a similarly sintered product prepared from coarser powders.

In accordance with the principles underlying the invention, specific quantities of metallic alloying components such as magnesium, silicon, lithium, etc., are provided, usually up to or even exceeding the maximum solid solubility limit, see Table B below. These constituents when added to the particulate mixture do not contaminate the mixture but function to expand the basic atomic structure of the Al in the course of sinterin-g to a degree inhibiting the tendency of the mixture to shrink and in fact, even expand the sintered part, when desired.

TABLE B Maximum Solid Solubility 1n Aluminum, Percent Additive Temperature, C

The invention also serves to produce sintered aluminous parts having exceptional mechanical properties and which are not as sensitive to the quench rate for ageing as per Mg.

By employing the invention, a sintered aluminous part can be produced which shows no surface discoloration. Thus a sintered aluminum alloy containing copper will when sintered in an atmosphere having a relatively high de'wpoint, say 20 F., exhibit a characteristic bronze surface discoloration. Magnesium additions improve surface appearance, the sintered surfaces becoming increasingly metallic in appearance as the magnesium content increases. At 0.3 w/o magnesium the surface is completely free of bronze discoloration and has a clean white metallic appearance despite the fact that relatively high dewpoint of F. was used in sintering. Improved color is thought to result from a thin film of magnesium oxide on the surface of the specimen this oxide lm also imparting higher hardness and good wear resistance to the sintered part-important where the parts are used in rubbing Contact with other parts. Also, where the sintered part is slightly porous one finds that the oxide is distributed throughout the structure as a result of partial oxidation of magnesium particles in the interior of the part. Thus satisfactory wear resistance is retained even after the surface oxide lms have been worn away. Such specimens can likewise exhibit improved high temperature properties as per oxide reinforcement of the matrix.

Before `giving specific examples of the invention, we shall first discuss the general principles underlying the invention.

I have found that by the addition of certain metallic elements which alloy with and do not contaminate the aluminum, that if the alloying process in the powder metallurgy of elementals or elementals and master alloys occurs such that there is an expansion of the Al atomic structure (either during the formation of any liquid phases or in the final solid state crystal lattice when the compact is cooled below the temperature where a liquid phase could exist) resulting from the addition of such additives as magnesium, silicon, lithium, etc., the shrinkage effect noted in connection as with Al-i-Cu mixtures (or in pure Al powders) is inhibited. Moreover, a gross expanision can be obtained by the proper addition of these expanding type elements. By placing the proper amount of additive in the aluminum blend, either in the form of an elemental or a master alloy; e.g., a 50-50 composition of aluminum-magnesium, an 11.6% Si balance Al alloy, etc. the contraction of the component (where shrinkage is not desired) can be not only minimized but controlled quite accurately.

In the case where expansion is required for high porosity, the amount needed for controlling contraction can be added and an excess put in such that there will be a gross expansion of the compact. This has been found to be true with additions of up to 0.5% to 1% magnesium as regards shrinkage, and up to 20% magnesium as regards expansion for Al or specific Al-Cu combinations and sizes of components. The amount needed for the exact control will vary with, among other parameters: the green density, the particle sizes of the powders, the quantity and type of the matrix metal as well as the contracting alloy additive (Cu, say, as powder or flake), the temperature, and the time of sintering, the sintering atmosphere and its characteristics, etc.

The quantity of the added element is not necessarily restrictive. Usually, as noted before, it is on the order of the maximum solid solubility at elevated temperatures where conventional sintering would take place. However, overages can Ebe placed into the mixtures as per the 20% magnesium 'which is above the maximum solid solubility of magnesium in aluminum, namely 14.9% at 451 C. The purpose of introducing overages is simply that with powder metallurgy compacts, complete alloy homogeneity is usually difficult to attain, and therefore, a maximum effect can be obtained by placing an overage in, such that a larger quantity of the added element will go into solution in a commercial time as regards sintering. Also, the counteracting forces are a function of the quantity of liquid phase formed, then the more of the additive put in, the better, because here the solid solubility limitation no longer is operative.

It should be noted again that a number of metals cause a contraction of the aluminum when they react with it and then go into solution. As such they exert the opposite effect noted above, and contribute to the overall shrinkage which normally occurs during the sintering process. Such contractive metals include: copper, manganese and Zinc.

It has likewise been found that highly reactive metals having virtually non-reducible oxide lms about them usually cannot be directly added to the aluminum matrix with optimum results being obtained. This is particularly true of magnesium. Best results are obtained when magnesium is prepared by atomization in an inert atmosphere such as helium. As such, the oxidation of the magnesium is at a minimum and it reacts quite readily with the aluminum and gives one the optimum effect. However, magnesium and magnesium-aluminum alloys which have been air-atomized or cast and pulverized in air, nevertheless do alloy with the aluminum, causing the sintered components to expand but optimum effects are not obtained because of the oxide lms involved.

Naturally, the magnesium which is tied up as oxide does not enter into the reaction and, in addition, tends to form diffusion-inhibiting barriers which slow down the reaction. The main reason that any reaction would occur at all is the fact that during green-pressing, some of the oxide is fractured such that there is intimate contact of the aluminum with the added metal. Also during heat-up (especially for uncompacted powders) the metal contained with the enveloping oxide film expands to a greater degree than the oxide film itself and crazes the oxide film such that metallic contact between particles can take place. In the formation of any liquid phases which may occur, such as eutectics, the liquid phase tends to pry up the oxide film, thus enhancing the diffusion rate between the aluminum and the additive.

It has likewise been found that the addition of metal particles with oxide coatings very difficult to reduce prior to or during sintering, when added directly to aluminum compacts has proven deleterious as the final sintered product has lower ductility, toughness and workabiiity. About the only time that such elements, eg., manganese and silicon, a metal and metalloid, respectively, can be effective is when the compact is severely green-pressed. At that time, the oxide is, in part, ruptured. This is a partially effective solution. Severe working of the compact after sintering and then heat-treating to put the additives into solution (assuming that the working operation has destroyed the effective inhibition of diffusion between the aluminum and the manganese or silicon as per their oxides), is about the best method of utilizing them. The same thing is true of other additives which contain virtually non-reducible oxide lms in conventional commercial atmosphere. The best way to handle such additives is as a master alloy; eg., aluminum-11.6% silicon-usually a brazing powder made of aluminum-silicon. Manganese also has some chance as a conventional additive, if put into the mix as a pre-alloy. However, aluminummanganese pre-alloyed powders are not commercially available in quantity and cheaply. In addition manganese is used here merely as an example of a metal with a hard to reduce oxide coating-it basically does not expand the crystal lattice of aluminum to counteract shrinkage effects as remarked upon previously.

Not only do we get this effect of expanded aluminum matrix, but if (A14-additive) intermetallics are formed which have a greater volume than the constituents which enter into the alloy itself, then there is a gross expansion which has the same effect as the expansion of the aluminum as noted.

Example I .-(Al-Mg) The basic mixture in the example is a blend of aluminous particulates with magnesium powder not in excess of 16% by weight, the magnesium powder being preferably ne enough to pass through a S-mesh screen, and being made by atomization in an inert atmosphere such as helium. The resultant blend is consolidated and bonded into a densied part by any of the following methods:

(1) The powders are pressed into a self-sustained compact and then sintered by rapidly heating to a temperature in the liquidus-solidus range in the presence of a protective or reducing atmosphere such as dry hydrogen, nitrogen, or dissociated ammonia. Sintering is carried out under conditions effecting the alloying and bonding of the particulates to produce a coherent mass. The conditions of time, temperature, pressed density and atmosphere determining the amount of atomic interdiffusion and reaction among particles which in turn determines the final properties of the material.

It is to be understood that hot and cold working can be used following the sintering operation to fully densify, extend alloy homogenization, to improve properties and to shape the part. Or the pressed and sintered part may be used directly, thereby saving additive manufacturing steps.

(2) An alternative method of consolidation of the particulates is to prepare pre-alloyed particulates in the form of needles or shot,- hot-molding them by applying heat and pressure simultaneously into a consolidated cake and then hot or cold working this cake into the finished'product.

(3) Still another method of consolidating and bonding is to cold or warm roll the powders below the recrystal- Iization temperatures, followed by alternative sinter-annealing and re-rolling until a fully densied material is obtained.

The amount of magnesium that can be put into the alloy is independent of the amount that would enter into solid solution.

A magnesium elemental addition also gives other advantages. It promotes sintering in poor atmospheres that would otherwise oxidize the particulates before they sinter together. This is because the magnesium lowers the melting temperature at the particulate surfaces and effectively starts sintering at the magnesium-aluminum eutectic temperature of 450 C. This is compared to 660 C. for the melting point of aluminum. In a three-constituent system (for example, the aluminum-magnesium-copper system), the melting would start at an even lower temperature. ln one example, in a sintering furnace with a minus 10 F. dewpoint atmosphere of dissociated ammonia, sintering could not be effected on 4% copper- 96% aluminum compacts, whereas in the same atmosphere, at the same heating rate and time, an addition of 0.3% magnesium effected the sintering.

Still another advantage of adding magnesium is that it acts to control the densification of the powder compact during sintering. With the proper combination of pressed density, sintering atmosphere and magnesium alloying content, the final dimensions of the sintered piece can be made to be smaller than the green piece, the same as the green piece, or grossly larger. The expanded pieces are particularly important for the production of parts where the density must be low, such as in porous bearings, or structural parts, or filter material.

Example 2.--(Al-Cu-Mg) The first step in making porous structures, such as bearings, or high-density structural parts formed of Al- Cu-Mg in accordance with the invention, involves mixing the powders. The mixture is composed of aluminum and copper particulates to which a small quantity of magnesium powder is added, and it is thoroughly intermingled, preferably with an organic lubricant.

In the case of copper powder or -copper flake, it is preferred to use a metal of good purity coupled vsn'th a high apparent density and a good flow rate The lubricant which is supplied to the powder mixture is added in a small amount, say up to 2% by weight, simply to eliminate powder pick-up by the die. Lubricant content may be varied depend-ing on the type of structure and the required density thereof. For example, Sterotex or Nopcowax contents as low as 1/2 w/o have been successfully employed and Nopcowax (an ashless type) as low as M; w/o when used with cast needles, either pure or pre-alloyed (2014).

Among the suitable mixtures are helium or air-atomized aluminum powder in mesh fractions from +40 through -325 mesh, mixed with 2% to 10% by Weight (and higher) copper in mesh fractions of 100/200 to 325, or as flake. One of the aluminum powders I have used is of the type which is air-atomized, such as Alcoa 120, having 30% to 40% -325 mesh particulates.

Other types of aluminum which are suitable include shot, needles and irregular flakes which can be used as large particulates and small particulates, below 1000 microns in size. Needles which have been succesfully employed in this method include Reynolds 200X, and 2014 and 7075 aluminum pre-alloyed needles.

The amount of magnesium added to the Al-Cu mixture is preferably in the ran-ge of 0.3% to 1% by weight, al-

g though I have successfully used `less than 0.3% magnesium (0.05%) and as high as 10%. With such additions, aluminum-copper mixtures may be successfully sintered without undue shrinkage and distortion to produce bearings and other products, e.g., high density parts of unusually high strength. The magnesium need not be introduced in elemental powder form, and may be in the form vcan be succesfully hardened to optimum strengths.

of a master alloy powder such as Mg-Al on a 50-50% or other basis.

The powder mixture is then compacted. Assuming that a sleeve is to be produced having an O.D. of .750 and an LD. of .4985, the compacting is effected by means of a die capable of producing the desired outside diameter, into which a core rod is inserted to establish the required inside diameter. To maintain uniform densication, equal top and bottom punch movements Vare used to obtain green densities of 50% to over 95% of theoretical at compacting pressures of 3 to 40 tons per square inch. Thus obtained from the die is a green compact in the shape of a sleeve or low-density bearing composed of aluminum-copper mixture, the integrity of the compact being sufficient for further handling.

The next step involves sintering of the green compact formed in the manner described above. The sintering technique may be that disclosed in the above-indentied patent applications, or any conventional batch or continuous sintering furnace arrangement. As is known from the phase diagram for the aluminum-copper system, as the copper content is raised, the amount of liquid phase presen-t in that alloy in the liquidus-solidus area at any given temperature also goes up. It has been found that distortion of the bearing or of any other Al-Cu part, whether of low or high density, may be effectively avoided by the use of magnesium additives.

The mangesium addition also acts to control the hardening and strengthing of the copper-aluminum alloys. These alloys harden by precipitating sub-microscopic particles of a secondary phase along the weak slip planes of the metal, locking or keying these weak points.

In conventional straight aluminum-copper alloys, the copper is dissolved into aluminum by heating to 500 C. and above, and quenching in cold water. The hardening by precipitation (also called aging) occurs naturally at room temperature (called the T-4 condition), or can be accelerated by heating to about 140 to 190 C. (called the T-6 condition). rl`his treatment causes submicroscopic particles to precipitate at the slip panes of the metal.

If the alloy is not quenched rapidly from the solution temperature, the precipitate will coalesce in particles too large for optimum hardening and strengthening, and further, the particles will form at the grain boundaries which can be detrimental.

The addition of small amounts of magnesium powder inhibits the precipitation at high temperature so that the drastic water quench is not mandatory. With magnesium, the secondary phase will more readily stay in solution upon air-cooling from the solution temperature. On the the air-cooling allows hardening of parts with close tolerances without the distortion and Warpage from a drastic cold-water quench from 500D C.

The -curves in FIGS. l, 2 and 3 show the aging characteristics for 4% copper-aluminum alloy with and without magnesium. FIGURE l, for 0.090 inch thick test bars, shows that the alloy containing magnesium (curve A) is initially at the same hardness as the straight copper alloy (curve B). After four days at room temperature, the water-quenched alloy with magnesium is harder than the water-quenched straight copper alloy.

In FIG. 2, for 0.4 inch thick specimens, the alloy with magnesium is softer after four days when air-cooled (curve C) than when water-quenched (curve D). However, both the air-cooled and water-quenched specimens are substantially better than the straight copper alloy that is water-quenched (curve E) or air-cooled (curve F). In this heavy thickness, the straight copper alloy even when quenched had a hardness of about 76 Rockwell H, and did no-t harden perceptibly.

FIGURE 3 illustrates the use of magnesium as a means to control the densification of aluminum powder metallurgy parts. This data (curve G) shows that for identical sintering conditions, the addition of 0.05 w/o of Imagnesium reduces the shrinkage by about three times from 0.95% to 0.3%. Larger additions of magnesium of more than 0.2 w/o reduce the shrinkage further and even cause the sintered dimensions to become larger than the green compact.

Example 3 (0r/1er additives, suc/z as silicon) Similar advantages are realized through the use of silicon rather than magnesium additions in the processing of aluminum powder-metallurgy parts. It has been observed for example, that aluminum p-owder parts containing 4 w/o copper .and 1/2 w/o lubricant will, if pressed to extremely high densities, i.e., upwards of 98% of theoretical, exhibit blistering ou sintering. The reason for this is that lubricant particles become sealed olf in non-interconnecting pores during cold-pressing to extremely high density. During heat treatment the lubricant vaporizes, expands, and unable to escape, raises or forms blisters on the surface and holes in the matrix of the sintered part. The addition of silicon and/or magnesium to the aluminum powder mix in concentrations up to 2 weight percent, can result in expansion of the compact during sintering, the amount of expansion depending on the quantity of silicon or magnesium added and the sintering conditions. As a result, lubricant entrapment and hence blistering can be minimized. This is evident from the data of Table C below.

TABLE C.-I3LISTERING CHARACTERISTICS OF POWDER FABRICATEI) ALUMINUM PARTS CONTAINING VARYING QUANTI'IIES OI? LUB RICANT ANI) MAGNESIUM. POWDER Composition oi Part Density Percent Severity of of Theoretical Blistering Aller Aluminum Type W /o Copper W/o Magnesium W/o Lubricant Sinter- Trpe Type 100% through 40 mesh, 40% 9G l -325 4 0 0 l 0&9 to Ell).0 Slight.

through 325 mesh.

9G fl 2 -325 lg l/ 97.7 t0 98.0 None to very slight. 9G 4 (J 0 99.2 Moderate.

1 Mesh flake. 2 Mesh.

other hand, the magnesium does not inhibit the precipitation at room temperature as it is in a non-equilibrium condition and must and can move toward equilibrium by precipiating.

The overall elect is that aluminum-copper-magnesium powder metallurgy parts can be air-cooled from the sintering temperature and still precipitate at room temperature to harden and strengthen.

Because cooling can be relatively slower, thicker parts Also,

so heavily encrusted with oxide that they cannot enter into a metallurgical reaction with the aluminum matrix just as pressed and sintered.) The inhibition to shrinkage, however, is nowhere near as marked as when magnesium is added in the same percentage, e.g., 0.5%. The reason is that the ensuing diminution in density, i.e., expansion as per magnesium, is very much greater than that for silicon. This can be seen if one uses the relatively crude parameter of starting density of magnesium and silicon additives themselves versus aluminum, which are, respectively, 1.74 g./cc., 2.33 g./cc. and 2.70 g./cc., i.e., the lower density additives when going into either solid state (crystal lattice) solution or forming a liquid phase with aluminum can and apparently usually cause the resultant phase to occupy a greater volume than the starting solid unreacted constituent, thereby creating expanding forces during this sintering stage.

It should be noted that all parameters entering into the total sintering process, e.g., time, temperature, dewpoint of the sintering atmosphere can be likewise adjusted to extend or inhibit the expansion force derivation or result. For instance, a very long time (relatively speaking) at temperature in a very low dewpoint atmosphere can cause the ultimate shrinkage of a compact where sucient porosity exists for the metal to ill by surface tension, plastic flow and dislocation and vacancy generation and flow mechanisms.

We have also had experience whereby quantities of aluminum added to an iron matrix have caused a similar expansion of powder compacts during sintering. In other words, the phenomenon associated with the atomic array expansion appears to be a universal one.

While there have been shown preferred techniques for fabricating aluminum-based products in accordance with the invention, it will be appreciated that many changes and modifications may be made therein without, however, departing from the essential spirit of the invention as defined in the annexed claims.

What is claimed is:

1. In a powder metallurgical process for the formation of aluminum-based articles comprising forming a powder mixture consisting essentially of particulate aluminum and from about l to by weight of the mixture of particulate copper, shaping the mixture and sintering at a temperature above the temperature at which a liquid phase rst appears, in a protective atmosphere, the improvement which consists essentially of controlling the shrinkage of the shaped mixture by adding to the mixture, before sintering, a component selected from the group consisting essentially of particulate magnesium-aluminum alloys and particulate magnesium in an amount suicient to impart to the mixture an amount of magnesium, within the range from 0.05 to 20% by weight, sufficient to at least partially counterbalance the shrinkage that would otherwise be exhibited by the shaped mixture during sintering.

2. The improvement of claim 1 in which a sucient amount of the said component is added to cause an expansion of the shaped mixture during sintering.

3, The improvement of claim 1 in which a sufficient amount of the said component is added to substantially counterbalance the shrinkage forces, thereby resulting in substantially no dimensional change during heating.

4. The improvement of claim 1 in which the components are present in an amount sufiicient to impart to the mixture a quantity of magnesium of from about 0.3% to about 1% by weight.

5. The improvement of claim 1 in which the components are present in an amount sufficient to impart to the mixture a quantity of magnesium of less than 0.3%.

6. In the method of producing aluminum based articles comprising shaping a powder mixture consisting essentially of particulate aluminum followed by sintering above 450 C. and cooling, the improvement which permits control over the amount of shrinkage consisting essentially of adding to the mixture before shaping and sintering, a component selected from the group consisting essentially of particulate magnesium and particulate aluminum-magnesium alloys in an amount to impart to the mixture a quantity of magnesium, Within the range from 0.05% to 20% by weight, suicient to at least partially counterbalance the shrinkage that would otherwise be exhibited by the shaped mixture.

7. The improvement of claim 6 wherein a sul'icient amount of said component is added to impart to the mixture a quantity of magnesium within the range from 0.05% to 0.3% by weight.

8. The improvement of claim 6 wherein a suflicient amount of said component is added to impart to the mixture a quantity of magnesium of about 0.3% by weight.

9. The improvement of claim 6 wherein a sufficient amount of said component is added to impart to the mixture a quantity of magnesium within the range from 0.3% to 1% by Weight.

10. The improvement of claim 6 wherein the amount of magnesium imparted to the mixture is suflcient to overcome al1 of the shrinkage.

11. The improvement of claim 6 in which the amount of magnesium imparted to the mixture is sufficient to cause an expansion of the shaped mixture.

References Cited by the Examiner UNITED STATES PATENTS 4/1939 Goetzel 75-200 6/1942 Jones 75--200 OTHER REFERENCES CARL D. QUARFORTH, Primary Examiner.

R. L. GRUDZIECKI, Assistant Examiner. 

1. IN A POWDER METALLURGICAL PROCESS FOR THE FORMATION OF ALUMINUM-BASED ARTICLES COMPRISING FORMING A POWDER MIXTURE CONSISTING ESSENTIALLY OF PARTICULATE ALUMINUM AND FROM ABOUT 1 TO 10% BY WEIGHT OF THE MIXTURE OF PARTICULAR COPPER, SHAPING THE MIXTURE AND SINTERING AT A TEMPERATURE ABOVE THE TEMPERATURE AT WHICH A LIQUID PHASE FIRST APPEARS, IN A PROTECTIVE ATMOSPHERE, THE IMPROVEMENT WHICH CONSISTS ESSENTIALLY OF CONTROLLING THE SHRINKAGE OF THE SHAPED MIXTURE BY ADDING TO THE MIXTURE, BEFOR SINTERING, A COMPONENT SELECTED FROM A GROUP CONSISTING ESSENTIALLY OF PARTICULATE MAGNESIUM-ALUMIUM ALLOYS AND PARTICULATE MAGNESIUM IN AN AMOUNT SUFFICIENT TO IMPART TO THE MIXTURE AN AMOUNT OF MANGESIUM, WITHIN THE RANGE FROM 0.05% TO 20% BY WEIGHT, SUFFICIENT TO AT LEAST PARTIALLY COUNTERBALANCE THE SHRINKAGE THAT WOULD OTHERWISE BE EXHIBITED BY THE SHAPED MIXTURE DURING SINTERING. 